This application claims the priority of 9-083541, filed Apr. 2, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a fuel injection apparatus and control method therefor. In particular, the present invention is suitable for a system for injecting fuel directly into the combustion chamber.
As for prior art apparatus, an engine having a fuel injection valve with a nozzle opening to the combustion chamber is disclosed in Japanese Patent Application Laid-Open No. 2-169834 (1990). In this fuel injection valve, a swing force is applied to the fuel flow in order to improve the granularity of the fuel mist and reduce the spray speed, and consequently prevent the fuel from depositing on a wall of the combustion chamber.
In the known fuel spray with its spray speed reduced, as the fuel spray is liable to be deflected due to the air turbulence (swirl/tumble) in the combustion chamber, and the fuel-air mixture can not be supplied stably to the neighboring area of the ignition plug, the fuel combustion tends to be unstable.
An object of the present invention is to provide a fuel injection apparatus and control method therefor in which the fuel-air mixture can be supplied to the neighboring area of the ignition plug without fuel spray deflection due to the air turbulence (swirl/tumble) in the combustion chamber and the fuel depletion on the combustion chamber wall is reduced as well, leading to soot reduction.
Another object of the present invention is to provide a fuel injection valve and a method of injecting fuel, by which the ignition can be improved, the production of soot can be reduced, and the stability of combustion can be improved when the engine speed is operating at high speed, even if the combustion is at a lean-burn state (i.e., an air/fuel ratio is about 20-50).
In order to achieve the above objects, a fuel injection valve having a nozzle opening to the combustion chamber inside and an ignition plug are provided so that the fuel injection valve may form fuel spray having different levels of average speed.
Preferably, the fuel injection valve forms relatively high-speed fuel spray at least in the half way of the single cycle of the fuel injection, and after that, it forms relatively low-speed fuel spray. Thus, the fuel-air mixture comprising high-speed fuel spray can be supplied to the neighboring area of the ignition plug.
Furthermore, a fuel injection valve for an engine is provided with a valve body, a valve seat, a nozzle opening and a fuel guide in a nozzle portion. In addition, the fuel guide forms a plurality of fuel swirling passages, each of which has different swirling strength.
Preferably, the fuel swirling passages which have less swirling strength are formed at the nozzle opening side, compared with fuel swirling passage which have larger swirling strength.
According to the present invention, the low-speed fuel spray does not deposit on the combustion chamber wall surface and the piston wall surface but diffuses in the combustion chamber and forms the fuel-air mixture. The fuel-air mixture formed with the high speed fuel spray supplied to the neighboring area of the ignition plug is ignited, and the generated flame kernel is propagated as well as diffused by spray force and air flow into the fuel-air mixture formed by the low-speed fuel spray. Consequently, it will be appreciated that the stabilization of combustion and the prevention of soot generation by reducing the deposition of fuel spray onto the combustion chamber wall surface and the piston wall surface can be established together.